Nosocomial or hospital acquired infections (HAI) have been estimated by the World Health Organization (WHO) to kill between 1.5 and 3 million people every year worldwide. Though commonly referred to as hospital acquired infections, nosocomial infections result from treatment in any healthcare service unit, and are generally defined as infections that are secondary to the patient's original condition. In the United States, HAIs are estimated to occur in 5 percent of all acute care hospitalizations, resulting in more than $4.5 billion in excess health care costs. According to a survey of U.S. hospitals by the Centers for Disease Control and Prevention (CDC), HAIs accounted for about 1.7 million infections and about 99,000 associated deaths in 2002. The CDC reported that “[t]he number of HAIs exceeded the number of cases of any currently notifiable disease, and deaths associated with HAIs in hospitals exceeded the number attributable to several of the top ten leading causes of death in U.S. vital statistics” (Centers for Disease Control and Prevention, “Estimates of Healthcare Associated Diseases,” May 30, 2007).
HAIs, including surgical site infections (SSIs), catheter related blood stream infections (CRBSIs), urinary tract infections (UTIs), ventilator associated pneumonia (VAP), and others, may be caused by bacteria, viruses, fungi, or parasites. Surgical site infections acquired in a hospital setting are commonly caused by bacterial organisms, such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. According to the CDC's Guideline for Prevention of Surgical Site Infections (1999), these species are ranked among the top five pathogens isolated from surgical site infections between 1986 and 1996. A ranking of the percentage distributions of infections that may be directly attributable to individual pathogen species may vary slightly between SSI, CRBSI, UTI, and VAP, but it is generally understood that less than about a dozen species are responsible for the vast majority of cases (see, e.g., National Nosocomial Infections Surveillance (NNIS) Report, Data Summary from October 1986-April 1996, May, 1996).
Ongoing efforts are being made to prevent HAI through, for instance, improved hand washing and gloving materials and techniques, but such efforts have met with limited success. In an effort to better understand and curb HAIs, government regulations have increased pressure on hospitals and care-givers to monitor and report these types of infections. However, these measures are further complicated due to the prevalence of outpatient services, a result of which being that many HAIs do not become evident until after the patient has returned home. As such, infection may proceed undiagnosed for some time, complicating treatment and recovery.
A need currently exists for improved methods for diagnosing HAI. Moreover, methods that could monitor a patient, for instance a patient's surgical site, in an outpatient setting, would be of great benefit.